NOTICE: this is the author’s version of a work that was accepted for publication in . Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Carbon [VOL 50, ISSUE 3, March 2012] DOI 10.1016/j.carbon.2011.11.002

GUEST EDITORIAL

Nomenclature of sp2 carbon nanoforms

Carbon’s versatile bonding has resulted in the discovery of a bewildering variety of nanoforms which urgently need a systematic and standard nomenclature [1]. Besides , nanotubes and , research teams around the globe now produce a plethora of carbon-based nanoforms such as ‘bamboo’ tubes, ‘herringbone’ and ‘bell’ structures. Each discovery duly gains a new, sometimes whimsical, name, often with its discoverer unaware that the same nanoform has already been reported several times but with different names (for example the nanoform in Figure 1i is in different publications referred to as ‘bamboo’ [2], ‘herringbone-bamboo’ [3], ‘stacked-cups’ [4] and

‘stacked-cones’ [5]). In addition, a single name is often used to refer to completely different carbon nanoforms (for example, the ‘bamboo’ structure in [2] is notably different from ‘bamboo’ in Ref

[6]). The result is a confusing overabundance of names which makes literature searches and an objective comparison of results extremely difficult, if not impossible.

There have been several attempts to bring order to the chaos of carbon nomenclature. An IUPAC subcommittee on carbon terminology and characterization that ran until 1991 produced a glossary of 114 terms for carbon materials. However the only carbon nanoforms included were fullerenes*

[7] and graphene† [8] (which remain the only carbon nanoforms defined in the IUPAC “Gold Book”

[9]), and this was in any case a list of defined terms rather than an attempt to classify carbon forms based on underlying shape. Following an international symposium on nanocarbons in Japan in

2002, Inagaki and Radovic proposed a nanocarbon nomenclature based on preparation methods

[10], drawing the important distinction between nano-structured and nano-sized carbon nanomaterials. However no definitions were given for detailed morphological differences.

* Defined by IUPAC as “Compounds composed solely of an even number of carbon atoms, which form a cage-like fused-ring polycyclic system with twelve five-membered rings and the rest six-membered rings. The archetypal example is [60], where the atoms and bonds delineate a truncated icosahedron. The term has been broadened to include any closed cage structure consisting entirely of three-coordinate carbon atoms.” doi:10.1351/goldbook.F02547 † Defined by IUPAC as “A single carbon layer of the structure, describing its nature by analogy to a polycyclic aromatic hydrocarbon of quasi infinite size. The term Graphene should be used only when the reactions, structural relations or other properties of individual layers are discussed.” doi:10.1351/goldbook.G02683 There are various ways that carbon nanoforms could be classified. These include their synthesis

conditions, physical properties such as density and internal surface area, or graphitic sheet texture

[11]. In the current editorial we attempt to develop a coherent nomenclature for carbon nanoforms

based on their morphological differences and the geometrical transformations that relate one form

to another.

The structurally simplest carbon nanoform is graphene. Graphene is a near planar sheet of sp2–

bonded carbon atoms in a hexagonal network. It can be considered as the final member of the

series of fused polycyclic aromatic hydrocarbons, such as naphthalene, anthracene and coronene.

Terms such as ‘single graphene layer’ and ‘graphene nanosheet’ are redundant since graphene is a

layer/sheet, always single and necessarily in the nanoscale as it is one atom thick. The preferable

term is simply ‘graphene’.

Graphene can serve as the initial building block for a series of thought experiments, generating

other carbon nanoforms by the application of geometrical transformations. Morphological

variation in sp2-based carbon nanoforms is a consequence of curvature, introduction of structural

defects, and dangling bonds. The result of this variation is deviation from ideal infinite planar-

sheet aromaticity, with corresponding localisation of states and variation in chemical reactivity.

We can classify an initial list of transformations as follows:

Stacked: one-dimensional ordered arrangement of multiple nanoforms of the same type (e.g. from

graphene to graphite). When a stack length is significantly larger than the dimensions of the

individual nanoform, the term ‘fibre’ can be applied.

Cut: breaking a line of C-C bonds, for example producing short segments from a longer nanotube

via a cut perpendicular to the tube axis, or graphene nanoribbons from graphene.

Circularly Wrapped: wrapping an object around an axis at a fixed distance, resulting in matching

edges (e.g. from graphene to a single-walled nanotube).

Scrolled: wrapping an object around an axis with continuously increasing distance, resulting in

mismatched edges, i.e. spirally wrapped (e.g. from graphene to a graphene nanoscroll).

2 Coiled: object wrapped around an axis with an additional translation along that axis.

Screwed: application of a screw dislocation along the periodic axis of a nanoobject or stack of

nanoobjects. For 0D nanoobjects a screw dislocation dipole is required. This typically converts a

stack of individual nanoobjects into continuous layers.

Coned: removal of an in-plane wedge of material, reconnecting any resultant dangling bonds,

resulting in pentagons at the apex (application of a wedge disclination).

By applying the various transformations listed above to graphene we created a carbon nanoform

“family tree” as shown in Figure 2. While the diagram is non-exhaustive (primarily for clarity), it

helps to classify the nanoforms by morphology, and provides a first step towards a standardised

nomenclature through use of these operations as adjectives to graphene. These transformations

result in families of forms as follows (names are preferentially selected based on shape rather than

analogy to everyday objects):

Nanotube: commensurately wrapped two-dimensional nanoform,

Nanoscroll: incommensurately wrapped two-dimensional nanoform,

Nanotoroid: commensurately wrapped one–dimensional nanoform,

Nanospiral: incommensurately wrapped one-dimensional nanoform,

Nanocone: nanoform constructed from one or more stacked conical layers,

Nanoribbon: layer subject to two parallel cuts resulting in a strip,

Platelet: layer cut in at least two directions giving a patch (e.g. polyaromatic hydrocarbon)

Fullerene: closed cage containing twelve pentagons*.

The description of the nanoforms given thus far can be further refined through the use of additional

terms, not included in the “family tree” since they can be applied to most of the forms already

there:

Single-/Double-/Multi-Walled: the wall of the nanoform consists of one, two, or multiple layers.

Hollow / Full-core: nanoform contains (/ does not contain) an interior cavity space equal to or

larger than twice the graphite inter-layer spacing.

3 Double-/Multi-cored: two or more nanoforms encapsulated in another nanoform of the same type.

Partitioned: hollow-core nanoform with internal walls orthogonal to the object axis which divide

the core into separate compartments.

Corrugated: the layer surface undulates without changing the overall shape of the nanoform. The

term applies when the scale of the undulations is less than the dimensions of the nanoform itself.

Wavy: the nanoform itself undulates. Thus the undulations in a wavy nanoform are on a larger

scale than in a corrugated nanoform.

Curved: a curved nanoform is considered as a wavy nanoform where the period of the undulations

is larger than the dimension of the nanoform

Polygonised: layers are facetted, without continuous curvature.

Collapsed: the distance between two otherwise separated points on a surface is reduced to

approximately that of the inter-layer spacing of graphite (typically due to Van der Waals

interaction).

Vertical / Horizontal: orientation of the principal axis of the object with respect to a horizontal

substrate.

Bundled: an ordered group of multiple approximately parallel one-dimensional nanostructures (e.g.

single-walled nanotube bundles).

Crystallised: aggregate of nanoforms of the same type possessing long-range order (e.g. fullerite).

Clustered: aggregates of nanoforms with no long- or short-range order besides that of the objects

themselves.

Closed / Open: object forms / does not form a continuous surface.

Open / Closed tip/edge: Object has / does not have functionalised or dangling bonds at its tip/edge.

For example closed-edge stacked platelets have carbon sheets which fold back on themselves, and

an open-tipped nanotube has terminating functionalised bonds at its ends.

4 Certain terms used previously in the literature are replaced here. In this system for example the

term ‘few layer graphene’ is incorrect and would be replaced by ‘few stacked ’. For

consistency with nanotubes, two and three stacked graphenes would be ‘double graphenes’ and

‘triple graphenes’ respectively. We propose the name ‘multi-walled fullerenes’ for multiply-

encapsulated closed carbon layer structures (commonly referred to as “carbon onions” or “nested

fullerenes”). While spherical structures such as those observed after extensive electron irradiation

are ‘multi-walled fullerenes’, hollow facetted nanoparticles (e.g. produced during arc-discharge)

would be ‘polygonised multi-walled fullerenes’. The terminology also distinguishes between

closed nanocones in a ‘dahlia’ type arrangement, which would be referred to as ‘clustered

nanocones’, from isolated individual multi-walled nanocones.

Scrolled structures, often misnamed ‘multi-walled nanoscrolls’, would be now ‘graphene

nanoscrolls’. This allows, for example, nanoscrolls from two stacked graphenes to be named

‘double graphene nanoscrolls’.

The term “herringbone” is often applied when the layers in a 1D nanoobject are at an angle to the

tube axis (resembling the skeleton of a fish), but does not distinguish different core structures. In

addition terms such as “herringbone nanotube” tend to link these nanoforms with conventional

parallel-walled nanotubes, whose surface chemistry is very different. We suggest instead

replacing the term “herringbone” with ‘stacked nanocones’, ‘hollow-core stacked nanocones’ and

‘partitioned stacked nanocones’ depending on the structure of the core. If the stacked cones form a

continuous layer they would be ‘screwed stacked nanocones’[12] and if the stack is sufficiently

long, it would be a ‘stacked nanocone fibre’. Another common term in the literature is “bamboo

nanotubes”, which in this nomenclature is replaced by terms such as ‘partitioned nanotubes’ and

‘partitioned stacked nanocones’. By the same logic, “nanobells” are now ‘stacked open multi-

walled fullerenes’. A full list of terminology from the literature and proposed standardised

nomenclature is given in Table 1.

5 The internal structure of a nanoform is revealed by transmission electron microscopy (TEM) which

produces a projected image of the nanostructure observed. For example high-resolution TEM of

carbon nanotubes provides valuable information concerning the number and orientation of the

graphenes. Based on high-resolution TEM images we classify various commonly observed one-

dimensional carbon nanoforms as indicated in Figure 3. The option clearly remains to add further

adjectives to refine description of the morphology, for example ‘incomplete’ if internal

compartments are broken. Figure 3 depicts schematic images for the forms shown in Figure 1,

and we note that these could also serve as standard symbols in chemical structure diagrams.

New nomenclature also needs to deal with hybrid carbon nanoforms consisting of two or more

carbon nanoforms. There are near infinite possible combinations of these, but the majority

observed experimentally to date can be classified either as one carbon nanoform filled with

another, or one nanoform attached to the outer surface of another. The notation used by the

fullerene community to describe endohedral fullerene structures is of the form ‘x@y’, where

species ‘x’ is positioned inside species ‘y’. We suggest the wider adoption of this convention, thus

for example “peapods” would instead be referred to as ‘fullerene-filled single-walled nanotubes’,

written as Cn@SWCNT [13], and one graphene nanoscroll encapsulated within another could be

written as CNS@CNS. In addition, this convention can be extended through the use of ‘//’ where

‘x//y’ indicates nanoform ‘x’ is attached to the exterior surface of nanoform ‘y’, where ‘x’ is

smaller than ‘y’. For example C60//SWCNTs would indicate C60 molecules grafted to the exterior

of a single-walled . We note that a similar scheme has been developed further to

provide a shorthand for other nanomaterial treatments such as doping [14,15].

This nomenclature can be extended to describe the chemical composition of heterogenous

carbon-based nanoforms. For example, a double-walled carbon nanotube containing substitutional

nitrogen would be written CNx-DWCNT, and COx-Graphene would be graphene oxide (graphene

with a highly oxidized basal plane) following this convention. Similarly heterogenous

6 nanomaterials, for example a single-walled carbon nanotube with domains of boron nitride would

be written as C(BN)x-SWCNT.

We have deliberately focussed here on sp2-bonded nanoforms, since nanodiamonds and carbynes

form separate categories of their own. This nomenclature could easily be extended further, for

instance, it is possible to imagine all of the forms discussed here built using other theoretically

proposed layered carbon structures such as haeckelites [16] and graphynes [17], as well as other

layered nanomaterials such as TiOx, MoS2 and BN. We have not discussed atomistic orientation

(nanotube chirality, graphitic stacking) since there are already well-defined terms for these.

The standardised nomenclature proposed here has been developed as a response to the mounting

variety and confusion within the world of carbon nanoforms. We hope it serves to provide a

coherent structure for carbon nanoform classification based on the underlying topology of the

objects. In this way it provides a convention which unambiguously describes most carbon

nanoforms, while remaining sufficiently flexible to adapt to new forms as they are discovered and

added to the ever-expanding carbon nanoform family tree.

We are aware that the resultant nomenclature proposed here can sometimes be more complex than

the common names currently in use. In the chemistry world it is quite easy to have alternative

common names for molecules such as ferrocene instead of bis(η5-cyclopentadienyl)iron.

Molecules are well-defined units but one should take care when adopting a similar route for carbon

nanoform nomenclature, where forms can have the same shape at the macroscopic scale but

atomically different variants. Thus if employing a common name it would be advisable to refer at

least once to the 'complete' name, for example, as defined in this article.

While we would not presume to develop here the ideal solution to carbon nomenclature, it is our

intention to raise awareness of the issue and stimulate debate. We hope that this editorial will

serve as a platform for future development of an exhaustive, definitive, yet flexible nomenclature,

7 hopefully through the medium of an authoritative body within the carbon community such as

IUPAC.

Acknowledgments

We are grateful to A. Schaper, P. Harris, M. Heggie, O. Chauvet, J. Hutchison, Y.Gogotsi and

P. Thrower, and especially M. Monthioux for useful comments, critical reading and discussion. We

are grateful to the Australian Research Council for the fellowship grant DP110104415 (ISM), the

Royal Society (NG), the European Commission under the Seventh Framework Programme

(FP7/2007-2013) under grant agreement no. 238363 (NG), the ERC Starting Grant (ERC-2009-

StG-240500) (NG), the EPSRC PIA Award (NG), and the French ANR project

NANOSIM_GRAPHENE (CPE) for financial support.

8 Figure 1. HRTEM of tubular nanoforms a) single-walled nanotube, b) double-walled nanotube, c) multi-

walled nanotube, d) scrolled graphene [18], e) hollow-core stacked nanocones, f) stacked curved platelet

fibre [3], g) full-core nanotube, h) stacked nanocones[3], i) partitioned stacked nanocones, j) stacked open

multi-walled fullerenes[4] and k) partitioned nanotube

Figure 2. “Family tree” of primary carbon nanoforms showing the topological relationships between them.

We note that all 1D forms can undergo the same operations as for the single-walled nanotube. For each

form further operations are also possible such as polygonisation (see text). In addition hybrid forms (such

as fullerene-filled nanotubes) are not included. Forms which have not been identified experimentally are

faded. A description of each operation can be found in the text.

9

Figure 3. Schematic of several one-dimensional forms from Figure 1 a) single-walled nanotube, b) double-

walled nanotube, c) multi-walled nanotube, d) scrolled graphene, e) hollow-core stacked nanocones, f) stacked curved platelet fibre, g) full-core nanotube, h) stacked nanocones, i) partitioned stacked nanocones,

j) stacked open multi-walled fullerenes and k) partitioned nanotube.

10

Molecular Forms (0 dimensions) [19] Soccerene, footballerene, buckyball, carbon bucky-cages Fullerene Multi-walled fullerene [20] Onions, bucky onions, nested fullerenes Single-walled nanocone [21] Nanohorn, nanocone Multi-walled nanocone [22] Nanocone Single-walled nanotube bundle toroid [23] Fullerene “crop-circle”, toroidal fullerene, nanohoop, carbon based toroid, doughnut shaped tube, nanotube ring, nanotorus Curved graphene platelet [24] Dome-shaped carbon, nanoislands Open fullerene [25] Bowl, bowl-shaped aromatic hydrocarbon, open-cage fullerene, bowlane Single-walled nanotube bundle nanospiral [26] Nanotube ring

Cylindrical nanoforms (1 dimensional) Single-walled nanotube [27] Single-layered nanotube, tubelenes, buckytubes, graphite microtubules Double-walled nanotube [15] Double-layer nanotube Multi-walled nanotube [28] “Russian doll” tubes, nested tubes, nested cylinder structures, coaxial cylinder structures Nanotube bundles [29] Nanotube ropes Graphene nanoscroll [30] Swiss roll tube, nanoscrolls, scroll nanotubes, scrolled graphene Collapsed nanotube [31] Dog bone nanotube, dumb-bell nanotube Stacked platelets [3] “Deck of Cards” fibre, nanofibre (hollow- or full-core) stacked nanocones [3] Stacked-cups, stacked cones, herringbone nanotube, herringbone nanofiber Screwed stacked nanocones [32] Stacked cones Partitioned nanotube [33] Bamboo nanotube, surface modulated nanotube Partitioned stacked nanocones [3] Bamboo, stacked-cups, stacked cones, herringbone, herringbone-bamboo, coalesced graphitic nanocones, conical layer nanotube, fishbone tube Stacked open multi-walled fullerenes [20] Nanobells, carbon nano-necklaces, necklaces of pearls structure, necklace-like hollow carbon nanospheres, surface modulated spherical layered nanotube Coiled nanotube [34] Helix-shaped nanotube, helical nanotube, corkscrew-like nanotube 11 Graphene nanoribbons [35]

Layered nanoforms (2 dimensional) Graphene [36] Graphene nanosheet, single graphene layer Double graphene [23] Bi-layer graphene Few stacked graphenes [23] Few-layers graphene, multi-layer graphene Vertically aligned few stacked graphenes [37] Nanowalls Disordered nanotube films [38] Buckypaper Vertically aligned nanotube arrays [39] Nanotube carpets, nanotube forests

Table 1. Proposed nomenclature with other names found in the literature in italics. This table aims to help

researchers in their literature searches, thus if employing a common name in an article it is suggested

to refer at least once to the standardised name, for example, as defined here. Note that only forms

reported experimentally in the literature are included in the table. References are to the first article which

definitively characterises the given nanoform.

[1] Grobert N. Carbon nanotubes – becoming clean. Materials Today 2007;10:28-35.

[2] Saito Y. Nanoparticles and filled nanocapsules. Carbon 1995;33:979-88.

[3] Monthioux M, Noé L, Dussault L, Dupin J.-C, Latorre N, Ubierto T, et al. Texturising and

structurising mechanisms of carbon nanofilaments during growth. J Mater Chem 2007;17:4611-8.

[4] Okuno H, Grivei E, Fabry F, Gruenberger TM, Gonzalez-Aguilar J, Palnichenko A, et al.

Synthesis of carbon nanotubes and nano-necklaces by thermal plasma process. Carbon

2004;42:2543–9.

[5] Munoz-Navia M, Dorantes-Davila J, Terrones M, Hayashi T, Kim YA, Endo M, et al. Synthesis

and electronic properties of coalesced graphitic nanocones. Chem Phys Lett 2005:407;327-32.

[6] Lee CJ, Park P. Growth model of bamboo-shaped carbon nanotubes by thermal chemical

vapor deposition. Appl Phys Lett 2000:77;3397-9.

12 [7] Godly EW, Taylor R. Nomenclature and terminology of fullerenes: a preliminary survey. Pure

& Appl Chem 1997: 69;1411-4

[8] Fitzer E, Kochling KH, Boehm HP and Marsh H. Recommended terminology for the

description of carbon as a solid (IUPAC Recommendations 1995). Pure Appl Chem. 1995: 67;

473-506

[9] IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Blackwell

Scientific Publications, Oxford (1997) compiled by A. D. McNaught and A. Wilkinson. XML on-

line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata;

updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook

[10] Inagaki M, Radovic LR. Nanocarbons. Carbon 2002:40;2263-84.

[11] Oberlin A. Carbonization and Graphitization. Carbon 1984;22:521-41

[12] Jaszczak JA, Robinson GW, Dimovski S, Gogotsi Y. Naturally occurring graphite cones.

Carbon 2003:41;2085-92

[13] Smith BW, Monthioux M, Luzzi DE. Carbon nanotube encapsulated fullerenes : a unique

class of hybrid materials. Chem Phys Lett 1999:315;31-6.

[14] Monthioux M, in „Meta-nanotubes“, Wiley VCH, ISBN #978-0-470-512182-1 (2011).

[15] Monthioux M, Flahaut E. Meta-and hybrid-CNTs: a clue for the future development of carbon

nanotubes. Mater Sci Eng C 2007:27;1096-101.

[16] Terrones H, Terrones M, Hernandez E, Grobert N, Charlier JC, Ajayan PM. New metallic

allotropes of planar and tubular carbon. Phys Rev Lett 2000:84;1716-9.

[17] Baughman RH, Eckhardt H, Kertesz M. Structure property predictions for new planar forms

of carbon – layered phases containing sp3 and sp atoms. J Chem Phys 1987:87;6687-99.

[18] Wu FY, Cheng HM. Structure and thermal expansion of multi-walled carbon nanotubes before

and after high temperature treatment. J Phys D 2005:38;4302-7

[19] Kratschmer, W. The infrared and Ultraviolet-absorption spectra of laboratory-produced carbon

dust-evidence for the presence of the C60 molecule. Chem Phys Lett 1990:170;167-70

13 [20] Ugarte D. Formation mechanism of quasi-spherical carbon particles induced by electron

bombardment. Chem Phys Lett 1993:207; 473-9.

[21] Iijima S, Yudasaka M, Yamada R, Bandow S, Suenaga K, Kokai F, et al. Nano-aggregates of

single-walled graphitic carbon nano-horns. Chem Phys Lett 1999:309;165-70.

[22] Krishnan A, Dujardin E, Treacy MM, Hugdahl J, Lynum S, Ebbensen,TW. Graphitic cones

and the nucleation of curved carbon surfaces. Nature 1997:388;451-4.

[23] Liu J, Dai H, Hafner JH, Colbert DT, Smalley RE, Tans ST, et al. Fullerene “crop circles”.

Nature 1997:385;780-1.

[24] Lacovig P, Pozzo M, Alfè D, Vilmercati P, Baraldi A, Lizzit S. Growth of dome-shaped

carbon nanoislands on Ir(111): the intermediate between carbidic clusters and quasi-free-standing

graphene. Phys Rev Lett 2009:103;166101

[25] Goto K, Holler M, Okazaki R. Synthesis and structure of a novel molecular bowl with an all-

carbon and acyclic framework. Tetrahedron Letters 1996:37;3141-4

[26] Martel R, Shea HR, Avouris P. Ring formation in single-wall carbon nanotubes. J Phys Chem

B 1999:103;7551-6.

[27] Iijima S, Ichihashi T. Single-shell carbon nanotubes of 1-nm diameter. Nature 1993:363;603-5.

[28] Iijima S. Helical microtubules of graphitic carbon. Nature 1991:354;56-8.

[29] Thess A, Lee R, Nikolaev P, Dai H, Petit P, Robert J, Xu C, Lee YH, Kim SG, Colbert DT,

Scuseria G, Tomanek D, Fisher JE, Smalley RE. Crystalline ropes of metallic carbon nanotubes.

Science 1996:273;483-7.

[30] Ruland W, Schaper AK, Hou H, Greiner A. Multi-wall carbon nanotubes with uniform

chirality: evidence for scroll structures. Carbon 2003:41;423-7.

[31] Motta M, Moisala A, Kinloch IA, Windle AH. High performance fibre from “dog bone”

carbon nanotubes. Adv Mat 2007:19;3721-6.

[32] Oberlin A, Rousseaux F. Graphitation partielle de quelques carbones durs (étude en

mircroscopie et microdiffraction électroniques). C R Acad Sci Paris 1967:265;436-9

14 [33] Blank VD, Gorlova IG, Hutchison JL, Kiselev NA, Ormont AB, Polyakov EV, et al. The

structure of nanotubes fabricated by carbon evaporation at high gas pressure. Carbon

2000:38;1217-40.

[34] Amelinckx S, Zhang XB, Bernaerts D, Zhang XF, Ivanov V, Nagy JB. A formation

mechanism for catalytically grown helix-shaped graphite nanotubes. Science 1994:265;635-9.

[35] Kosynkin DV, Higginbotham AL, Sinitskii A, Lomeda JR, Dimiev A, Price BK, et al.

Longitudinal unzipping of carbon nanotubes to form graphene nanoribbons. Nature 2009:458;872-

6.

[36] Novoselov KS, Geim AK, Morozov SV, Jiang D, Zhang Y, Dubonos SV, Grigorieva IV,

Firsov AA. Electric field effect in atomically thin carbon films. Science 2004:306;666-9.

[37] Wu Y, Qiao P, Chong T, Shen Z. Carbon nanowalls grown by microwave plasma enhanced

chemical vapor deposition. Adv Mat 2002:14;64-7.

[38] Endo M, Muramatsu H, Hayashi T, Kim YA, Terrones M, Dresselhaus NS. “Buckypaper”

from coaxial nanotubes. Nature 2005:433;476.

[39] Wu TC, Chang SH. Temperature enhanced growth of ultralong multi-walled carbon nanotubes

forest. Curr Appl Phys 2009:9;1117-21.

Irene Suarez-Martinez

Institute des Matériaux Jean Rouxel, CNRS-, Université de Nantes, BP 32229, 44322 Nantes,

France and

Nanochemistry Research Institute, Curtin University, GPO BOX U1987, Perth, 6845, Australia

Nicole Grobert

Department of Materials, University of Oxford, Oxford, OX1 3PH, UK

Christopher P. Ewels

Institute des Matériaux Jean Rouxel, CNRS-, Université de Nantes, BP 32229, 44322 Nantes,

France

15